This section is from the book "The Horse - Its Treatment In Health And Disease", by J. Wortley Axe. Also available from Amazon: The Horse. Its Treatment In Health And Disease.
This vessel descends on the inner aspect of the humerus and distributes branches to the muscles of the upper arm and other adjacent structures, the larger and more important of which are -
1. Prehumeral, or Anterior Circumflex.
2. Deep Humeral, or Humeralis Profunda.
4. Artery of the Biceps.
On nearing the upper extremity of the radius or forearm the humeral artery divides into two unequal branches, the anterior and posterior radials: one, the smaller anterior radial, passes in a forward direction, and after distributing several small vessels to the extensor muscles, courses its way down the front of the leg as far as the knee, to which it furnishes numerous small branches.
The Posterior Radial, much more voluminous than the anterior, descends on the inner side of the radius or forearm, where it is covered by the flexor metacarpi interims muscle. In its course along the limb the posterior radial gives off branches to the elbow-joint, the flexor and extensor muscles, the skin, and also to the knee-joint. On reaching the latter it divides into two: (l.) The small Metacarpal Artery. (2.) The large Metacarpal Artery. The former, superficially placed at first on the inner side of the knee, dips down behind the head of the canon-bone. It crosses to the outer side by passing between the suspensory and the subcarpal ligament. Here it anastomoses with a branch from the supra-carpal arch to form the subcarpal arch, which then proceeds to give off the anterior and posterior interosseous arteries, which supply blood to the structures behind and in front of the canon-bone, to the bone itself, to its periosteum or covering, and to the flexor tendons.
The large metacarpal artery descends on the inner side and somewhat in front of the flexor tendons until it reaches the sesamoid bones, where it divides into two parts, the internal and external digital arteries. These vessels pursue a downward course over the fetlock-joint, giving off branches before and behind to the tissues in the region of the pastern, and finally, entering the foot, they break up into a number of vessels and supply the frog, the coronary cushion, the sensitive laminae, the coffin-bone, and other parts contained within the hoof. This artery is situated between the plantar nerve behind and the internal metacarpal vein in front.